The objective of this proposal is to study the role and signaling mechanisms by which the kallikreinkinin system (KKS) protects against salt-induced nephrosclerosis. The long-term goal is to develop novel therapeutic targets in the treatment and prevention of chronic renal disease and end-stage renal failure. Renal kallikrein levels are markedly reduced in humans and animal models with renal disease. By linkage analysis, we showed an association of a promoter polymorphic allele in the human tissue kallikrein gene with salt-induced hypertension and end-stage renal failure, as well as with blood pressure responses to changes in dietary sodium restriction. These findings implicate an important role of the KKS in salt-sensitive hypertension and renal function. Indeed, our preliminary studies show that elevated kallikrein/kinin levels (following kallikrein gene transfer) results in suppression of salt-induced inflammatory cell infiltration, glomerular enlargement, apoptosis, cell proliferation and collagen content in Dahl salt-sensitive (DS) rats. These protective effects were accompanied by increased nitric oxide (NO) levels and reduced oxidative stress and TGF-beta expression. Based on these findings, we hypothesize that the KKS through NO formation prevents and reverses salt-induced nephrosclerosis through inhibition of oxidative stress-induced signaling pathways. The following Specific Aims will be pursued to determine the signaling mechanisms that mediate the protective effects of the KKS in: 1) interstitial inflammation, 2) apoptosis, 3) proliferation and hypertrophy and 4) extracellular matrix accumulation leading to fibrosis. The signaling mechanisms may involve MCP-1, VCAM-1, ICAM-1, NF-kappaB, TGF-beta, MAPK, PA/MMP, PI3-kinase/Akt and p21/p27kip1. Enhanced kallikrein levels will be achieved by kallikrein gene delivery and kallikrein protein infusion into a salt-dependent hypertensive rat model. Cellular signaling pathways will be dissected in cultured endothelial and renal cells using specific inhibitors, neutralizing antibodies, dominant-negative DNA constructs, and small interference RNA. These studies should provide novel and in-depth information regarding the role of kallikrein/kinin in prevention and reversal of inflammation, apoptosis, proliferation, hypertrophy, and fibrosis that contribute to salt-induced nephrosclerosis.